Method for pre-deoxidizing and alloying molten steel by using calcium carbide for converter direct upper continuous steel casting

Abstract

The invention belongs to the field of steelmaking, and relates to a method for pre-deoxidizing and alloying molten steel by using calcium carbide for converter direct up-continuous steel casting, which comprises the following steps: adopting a calcium carbide raw material with the CaC2 content of more than or equal to 70% and the particle size of 5-20mm, and ensuring that the material is dry and stable through four-layer damp-proof packaging and transportation of a dangerous chemical special vehicle; before converter tapping, calcium carbide is added into an empty steel ladle filled with stuffing sand, the adding amount is calculated according to the formula of (end point oxygen content-calcium carbide equilibrium oxygen content 200 ppm) * 0.56, and 30-60 kg of aluminum or 50-110 kg of high-aluminum iron is replaced; and in the tapping process, aluminum / high-aluminum iron, silicon-manganese alloy and lime are sequentially added, argon is blown from the bottom after tapping, stirring is conducted for 10-20 minutes, aluminum wires, calcium wires and the like are supplemented, and refining is completed. Through the calcium carbide pre-deoxidation process, the use amount of an aluminum-based deoxidizer is reduced, generation of Al2O3 inclusions is reduced, the cleanliness of molten steel is improved, meanwhile, the cost is saved by about 3.8 yuan per ton of steel, and the method is suitable for converter direct continuous casting production of low-medium carbon steel and low-alloy steel, does not need LF refining treatment and has remarkable economic benefits and process applicability.

Description

Technical Field

[0001] The present invention belongs to the field of steelmaking, and relates to a method for pre-deoxidizing and alloying molten steel with calcium carbide for continuous casting steel grades directly from a converter. Background Art

[0002] In the field of steelmaking, converter steelmaking is a widely used process method. During the converter steelmaking process, the deoxidation and alloying of molten steel are two crucial steps. Deoxidation is to reduce the content of free oxygen in the molten steel, prevent defects from being generated due to oxidation during the solidification of the molten steel, and at the same time help improve the purity and quality of the molten steel. Alloying is to adjust the chemical composition of the molten steel to meet the specific requirements of different steel grades for composition.

[0003] In traditional converter steelmaking deoxidation processes, the commonly used deoxidizers mainly include ferroalloys containing Si, Al, Mn, such as ferrosilicon, ferraluminum, high-carbon ferromanganese, etc. According to the different steel grades, deoxidizing and alloying materials such as silicomanganese alloy, pure aluminum, low-carbon ferromanganese, metallic manganese, calcium silicate alloy, etc. are also used. These deoxidizers react chemically with the oxygen in the molten steel during the converter steelmaking process to achieve the purpose of deoxidation. At the same time, by adding ferroalloys with different components, the chemical composition of the molten steel can also be adjusted to meet the requirements of subsequent processes and the final product.

[0004] However, there are also some problems in the use of traditional deoxidizers. For example, high-aluminum deoxidizers such as ferraluminum have good deoxidation effects, but they have high costs, and the large-scale use will lead to an increase in Al2O3-type inclusions in the molten steel, affecting the purity and quality of the molten steel. In addition, some deoxidizers such as calcium silicate alloy also have certain safety hazards during production, transportation and storage, and require strict management and control.

[0005] Calcium carbide (CaC2), as a potential deoxidizer, mainly consists of CaC2 and contains a certain amount of impurities. During the steelmaking process, calcium carbide can react chemically with the oxygen in the molten steel to generate calcium oxide and carbon monoxide gas, thereby achieving the purpose of deoxidation. At the same time, calcium carbide also has a certain alloying effect and can adjust the chemical composition of the molten steel. However, due to the strict management requirements for the production, transportation and storage of calcium carbide, traditionally it is mostly applied in LF refining furnaces as slag-making deoxidizing materials, and is less used in steel grades without the refining furnace refining process.

[0006] However, with the continuous progress of steelmaking technology and the increasing requirements for the quality of molten steel, people have begun to explore the application of calcium carbide in the deoxidizing alloying process of continuous casting steel grades directly from converters. By improving the particle size, packaging, transportation, and on-site storage conditions of calcium carbide, as well as optimizing process parameters such as the feeding device and alloy addition timing during converter steelmaking, it is expected to achieve the effective application of calcium carbide in continuous casting steel grades directly from converters, further improving the quality of molten steel and production efficiency.

[0007] Therefore, developing a method for pre-deoxidizing and alloying molten steel with calcium carbide for continuous casting steel grades directly from converters has important technical significance and economic value. Summary of the Invention

[0008] In view of this, the purpose of the present invention is to provide a method for pre-deoxidizing and alloying molten steel with calcium carbide for continuous casting steel grades directly from converters to solve the above problems.

[0009] To achieve the above object, the present invention provides the following technical solution: A method for pre-deoxidizing and alloying molten steel with calcium carbide for continuous casting steel grades directly from converters, characterized by including the following steps:

[0010] S1. Prepare calcium carbide raw materials: The content of CaC2 ≥ 70%, CaO ≤ 20%, P ≤ 0.80%, S ≤ 0.25%, and the particle size is controlled within the range of 5 - 20 mm, where the proportion of particles with a size of 5 - 20 mm ≥ 90%, and the total proportion of particles > 20 mm ≤ 10%;

[0011] S2. Package calcium carbide: Use small bags for packaging, with each bag weighing 10 ± 0.2 kg. The inner layer of the small bag is a plastic film, and the outer layer is a plastic woven bag; every 100 small bags are packed into a ton bag. The inner layer of the ton bag is a plastic film, and the outer layer is a plastic woven bag. The packaging is intact without water stains or oil stains on the surface;

[0012] S3. Transport and storage: Use a special truck for hazardous chemicals in a box for transportation, and set a moisture-proof tray support at the bottom of the carriage; stack it in a well-ventilated and dry area on-site, set up moisture-proof shielding, and the stacking amount ≤ 10 tons, and pick it up as needed;

[0013] S4. Calcium carbide addition method: Before tapping from the converter, after filling the empty ladle with tundish powder, calcium carbide is put into the ladle through the feeding hopper and the blanking pipe added to the rear platform of the converter;

[0014] S5. Calculate the calcium carbide addition amount: According to the formula "Calcium carbide particle addition amount (kg / furnace) = (Final oxygen content - Calcium carbide equilibrium oxygen content 200 ppm) × 0.56", the single-furnace addition amount is 110 - 230 kg, replacing 30 - 60 kg of aluminum or 50 - 110 kg of high-aluminum iron;

[0015] S6. Alloying operation sequence:

[0016] S61. After filling the empty ladle with starter powder, calcium carbide is added.

[0017] S62. When tapping from the converter until the molten steel in the ladle reaches 1 / 2 of the ladle capacity, aluminum or ferrosilicon-aluminum is added.

[0018] S63. Ferrosilicon, ferromanganese or silicomanganese alloy is added.

[0019] S64. When tapping until the molten steel reaches 3 / 4 of the ladle capacity, lime is added.

[0020] S7. Molten steel treatment: After tapping is completed, the ladle car is moved to the argon blowing station for bottom argon blowing and stirring for 10 - 20 minutes. During this period, aluminum wire, carbon powder cored wire, ferrotitanium wire and calcium wire are added additionally until the molten steel composition and temperature are qualified, and then it is hoisted to the continuous casting process for pouring.

[0021] Optionally, in the calcium carbide particle size, the proportion of particles with a size of 5 - 10 mm is ≥60%, and the proportion of particles with a size of 10 - 20 mm is ≤40%.

[0022] Optionally, the addition amount of the lime is 0.2 - 0.5% of the weight of the molten steel.

[0023] Optionally, this method is applicable to the converter direct - continuous casting production of medium - low carbon structural steel and low - alloy structural steel without passing through the LF refining furnace treatment.

[0024] Optionally, after adding calcium carbide, the Al₂O₃ inclusions generated by molten steel deoxidation are reduced, the oxygen content of the active oxides in the ladle top slag is decreased, and the number of casting heats in the continuous casting tundish is increased.

[0025] Optionally, there is no gap between the outer plastic woven bag and the inner plastic film of the ton - bag for packaging calcium carbide, and the ton - bags are stacked with the support of a pallet rack.

[0026] Optionally, during the refining process in the argon blowing station, the bottom argon blowing stirring intensity is 200 - 400 NL / min, and the stirring time is not less than 8 minutes.

[0027] The beneficial effects of the present invention are as follows:

[0028] The chemical composition design is scientific and reasonable: This method uses calcium carbide with specific particle size and chemical composition as a deoxidizer, ensuring the stability and reliability of the deoxidation effect. By precisely controlling the particle size of calcium carbide, the reaction rate and deoxidation efficiency with molten steel can be optimized, thereby improving the quality of molten steel.

[0029] Good physical properties: As an efficient deoxidizer, calcium carbide has excellent physical properties. Its high hardness and high density enable it to quickly react with the oxygen in molten steel during deoxidation to form stable oxides, effectively removing the free oxygen in molten steel.

[0030] Wide range of materials and safe, environmentally friendly and controlled use: The raw material of calcium carbide has a wide source and is easy to obtain. At the same time, through the adoption of four-layer moisture-proof packaging and strict transportation and storage management measures, the safety and environmental friendliness of calcium carbide during use are ensured, avoiding quality decline and safety risks caused by problems such as moisture absorption and pollution.

[0031] Good effect on pre-deoxidation and alloying of molten steel: This method utilizes the good deoxidation ability of calcium carbide to achieve effective pre-deoxidation of molten steel. At the same time, calcium carbide also has a certain alloying effect, which can adjust the chemical composition of molten steel to meet the specific requirements of different steel grades for composition.

[0032] Significantly improved cleanliness of molten steel: After deoxidation and alloying using this method, the inclusion content in molten steel is significantly reduced, and the cleanliness is significantly improved. This helps to reduce the defects generated by oxidation during the solidification of molten steel and improve the quality and performance of steel.

[0033] Low application cost: Compared with traditional deoxidizers such as high-aluminum materials like ferrosilicon aluminum, the cost of calcium carbide is lower. By using calcium carbide for deoxidation and alloying, the production cost can be significantly reduced, and the economic benefits of enterprises can be improved.

[0034] Promote the innovation and development of the steelmaking process: The successful application of this method provides new ideas and technical support for the innovation and development of the steelmaking process. By continuously optimizing and improving the calcium carbide deoxidation and alloying process, the progress and upgrading of steelmaking technology can be further promoted.

[0035] In summary, the method of using calcium carbide for pre-deoxidation and alloying of molten steel for converter-directly-connected continuous casting steel grades has significant technical advantages and economic value, and is of great significance for improving the quality and production efficiency of molten steel, reducing production costs, and promoting the innovation and development of the steelmaking process.

[0036] Other advantages, objectives and features of the present invention will be described to some extent in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. Detailed implementation manners

[0037] The following specific examples illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. Specific embodiments

[0039] The following takes the application example of producing Q235B low-carbon structural steel by a 225-ton converter in a steel plant (direct continuous casting process, without passing through LF refining) as an example to illustrate the specific implementation process of this method in detail:

[0040] Example 1: Carbide pre-deoxidation alloying of Q235B low-carbon steel

[0041] 1. Preparation of calcium carbide raw materials

[0042] Composition requirements: CaC2 content is 72%, CaO content is 18%, P content is 0.05%, S content is 0.15%, and the balance is impurities.

[0043] Particle size control: Obtain 5-20mm particles through crushing and screening, among which 5-10mm accounts for 65%, 10-20mm accounts for 30%, and the total proportion of particles <5mm and >20mm is 5%.

[0044] 2. Packaging and transportation

[0045] Adopt four-layer moisture-proof packaging:

[0046] Small bag (10±0.2kg): The inner layer is a polyethylene film bag, and the outer layer is a polypropylene woven bag, sealed without damage;

[0047] Ton bag: Every 100 small bags are packed into a ton bag lined with polyethylene film, and the outer layer is a polypropylene woven bag.

[0048] Transportation: Use a special truck for hazardous chemicals for transportation. A wooden moisture-proof pallet is set at the bottom of the carriage. Store it in a dry area of the steelmaking workshop on-site. The stacking quantity is 8 tons, and it is taken as needed.

[0049] 3. Operation of adding calcium carbide

[0050] Adding time: Before tapping the converter, after filling the empty ladle with tapping sand, calcium carbide is put into the bottom of the ladle through the feeding hopper and the feeding pipe added to the platform behind the furnace.

[0051] Calculation of adding amount:

[0052] The oxygen content at the end of the converter is 550ppm, the equilibrium oxygen of calcium carbide is 200ppm, and the molten steel volume is 225 tons. Calculate according to the formula:

[0053] Calcium carbide amount = (550 - 200)×0.56 = 196kg

[0054] The actual added amount is adjusted to 200kg / furnace, replacing 60kg of aluminum in the original process.

[0055] 4. Alloying operation process

[0056] Step sequence:

[0057] a. After the ladle is filled with sand, add 200 kg of calcium carbide;

[0058] b. When tapping from the converter into the ladle until the molten steel volume in the ladle reaches 112.5 tons (1 / 2 volume), add the remaining 1.00 kg / t of aluminum;

[0059] c. Add ferrosilicon manganese alloy (SiMn: 2.40 kg / ton of steel) and recarburizer 1.30 kg / t;

[0060] d. When tapping until the molten steel volume reaches 168.75 tons (3 / 4 volume), add 450 kg of lime (0.2% of the molten steel volume);

[0061] e. After tapping is completed, move the ladle car to the argon blowing station, stir with bottom argon blowing, the argon flow rate is 300 NL / min, for 15 minutes. During this period, add 0 m of aluminum wire and 350 m of calcium wire.

[0062] 5. Effect verification

[0063] Cost saving: Save 0.26 kg of aluminum per ton of steel, reduce the cost by 2.73 yuan / ton of steel;

[0064] Molten steel cleanliness: The total oxygen content of the molten steel is reduced from 35 ppm in the original process to 28 ppm, and the Al2O3 inclusions are reduced by 30%;

[0065] Process stability: The calcium carbide reaction is complete, and the carbon increase in the molten steel ≤ 0.003%;

[0066] Continuous casting effect: The number of casting furnaces in the continuous casting tundish is increased from 18 furnaces in the original process to 25 furnaces, and no nozzle clogging occurs.

[0067] Example 2: Calcium carbide pre-deoxidation alloying of Q355 low alloy steel

[0068] (Slightly, the implementation steps are similar to those in Example 1, and the parameters are adjusted as follows:)

[0069] Calcium carbide addition amount: The end point oxygen is 600 ppm, the molten steel volume is 220 tons, the addition amount is 220 kg, replacing 100 kg of high-aluminum iron;

[0070] Alloying: When 1 / 2 of the molten steel is tapped, add 1.65 kg of high-aluminum iron (Al ≥ 50%), 0.58 kg / t of ferrosilicon, 8.50 kg / t of ferrosilicon manganese alloy, and 1.50 kg / t of recarburizer;

[0071] Effect: The sulfur content of the molten steel is reduced from 0.025% to 0.018%, and the cost per ton of steel is reduced by 2.86 yuan.

[0072] The method of pre-deoxidizing and alloying molten steel with calcium carbide for the steel grades directly from converter to continuous casting has the advantages of scientific and reasonable chemical composition design, good physical properties, wide range of materials, safe, environmentally friendly and controlled use, good effect of pre-deoxidizing and alloying molten steel, significant improvement in molten steel cleanliness, and low application cost, and the practical effect is ideal.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the present technical solution, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for pre-deoxidizing and alloying molten steel with calcium carbide for converter-directly-connected continuous casting steel grades, characterized in that, It includes the following steps: S1. Prepare calcium carbide raw materials: the CaC2 content is ≥70%, CaO ≤20%, P ≤0.80%, S ≤0.25%, the particle size is controlled within the range of 5 - 20 mm, where the proportion of particles with a size of 5 - 20 mm is ≥90%, and the total proportion of particles >20 mm is ≤10%; S2. Package calcium carbide: Use small bags for packaging, with each bag weighing 10 ± 0.2 kg. The inner layer of the small bag is a plastic film, and the outer layer is a plastic woven bag; every 100 small bags are packed into a ton bag. The inner layer of the ton bag is a plastic film, and the outer layer is a plastic woven bag. The packaging is intact without water stains or oil stains on the surface; S3. Transport and storage: Use a special truck for hazardous chemicals in the box for transportation, and a moisture-proof tray support is set at the bottom of the carriage; Stack it on the site in a ventilated and dry area, set up moisture-proof shelters, and the stacking quantity is ≤10 tons, and it can be taken as needed; S4. Method of adding calcium carbide: Before tapping in the converter, after filling the empty ladle with tapping sand, calcium carbide is put into the ladle through the feeding hopper and the feeding pipe added to the rear platform of the converter; S5. Calculation of the addition amount of calcium carbide: According to the formula "the addition amount of granular calcium carbide (kg / furnace) = (the oxygen content at the end point - the balanced oxygen content of calcium carbide 200 ppm) × 0.56", the addition amount per furnace is 110 - 230 kg, replacing 30 - 60 kg of aluminum or 50 - 110 kg of high-aluminum iron; S6. Alloying operation sequence: S61. After filling the empty ladle with tapping sand, add calcium carbide; S62. When the molten steel in the converter is tapped to reach 1 / 2 of the ladle capacity, add aluminum or high-aluminum iron; S63. Add ferrosilicon, ferromanganese or silicomanganese alloy; S64. When the tapping reaches 3 / 4 of the molten steel volume, add lime; S7. Molten steel treatment: After tapping, the ladle car is moved to the argon blowing station for bottom argon blowing and stirring for 10 - 20 minutes. During this period, add aluminum wire, carbon powder cored wire, ferrotitanium wire and calcium wire until the composition and temperature of the molten steel are qualified and then it is hoisted to the continuous casting process for pouring.

2. The method for pre-deoxidizing and alloying molten steel with calcium carbide for converter-directly-connected continuous casting steel grades according to claim 1, wherein: In the particle size of the calcium carbide, the proportion of particles with a size of 5 - 10 mm is ≥60%, and the proportion of particles with a size of 10 - 20 mm is ≤40%.

3. The method for pre-deoxidizing and alloying molten steel with calcium carbide for converter-directly-connected continuous casting steel grades according to claim 1, characterized in that: The addition amount of the lime is 0.2 - 0.5% of the weight of the molten steel.

4. The method for pre-deoxidizing and alloying molten steel with calcium carbide for converter-directly-connected continuous casting steel grades according to claim 1, characterized in that: The method is applicable to the converter direct continuous casting production of medium and low carbon structural steel and low alloy structural steel without passing through the LF refining furnace treatment.

5. The method for pre-deoxidizing and alloying molten steel with calcium carbide for converter-directly-connected continuous casting steel grades according to claim 1, characterized in that: After adding calcium carbide, the Al2O3 inclusions generated by the deoxidation of the molten steel are reduced, the oxygen content of the active oxides in the top slag of the ladle is decreased, and the number of casting furnaces in the continuous casting tundish is increased.

6. The method for pre-deoxidizing and alloying molten steel with calcium carbide for converter-directly-connected continuous casting steel grades according to claim 1, characterized in that: There is no gap between the outer plastic woven bag and the inner plastic film of the ton bag for packaging calcium carbide, and the ton bag is supported by a tray support during stacking.

7. The method for pre-deoxidizing and alloying molten steel with calcium carbide for converter-directly-connected continuous casting steel grades according to claim 1, characterized in that: During the refining process in the argon blowing station, the stirring intensity of bottom argon blowing is 200 - 400 NL / min, and the stirring time is not less than 8 minutes.